Thin film formation method

ABSTRACT

A thin film formation method to form an amorphous silicon film containing an impurity on a surface of an object to be processed in a process chamber that allows vacuum exhaust includes supplying a silane-based gas composed of silicon and hydrogen into the process chamber in a state that the silane-based gas is adsorbed onto the surface of the object without supplying an impurity-containing gas, supplying the impurity-containing gas into the process chamber to form the amorphous silicon film containing the impurity without supplying the silane-based gas, and performing the supplying of the silane-based gas and the supplying of the impurity-containing gas alternately and repeatedly such that the impurity reacts with the silane-based gas.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional application of prior U.S. applicationSer. No. 13/095,503, filed on Apr. 27, 2011, which claims the benefitsof Japanese Patent Application No. 2010-106031, filed on May 1, 2010 andJapanese Patent Application No. 2011-043771, filed on Mar. 1, 2011, inthe Japan Patent Office, the contents of which are incorporated hereinin its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a film formation method which forms athin film containing an impurity on a surface of an object to beprocessed such as a semiconductor wafer or the like.

2. Description of the Related Art

In general, various processes, such as film formation, etching,oxidation, diffusion, surface modification, native oxide removal, or thelike, are performed on a semiconductor wafer including a siliconsubstrate or the like in order to manufacture a semiconductor integratedcircuit. From among the various processes, film formation will beexemplarily explained. During manufacture of a semiconductor integratedcircuit, for example, a DRAM or the like, film formation process may beperformed by forming recess portions, such as contact holes,through-holes, wiring grooves, cylindrical grooves of a capacitor havinga cylindrical structure, or the like, in an insulating film formed on asurface of a semiconductor wafer and filling the recess portions with aconductive thin film.

A silicon film containing an impurity has been conventionally used asthe thin film filled in the recess portions, because the silicon filmhas a relatively good step coverage and a relatively low cost. A methodof filling the recess portions will be explained with reference to FIGS.12A and 12B. FIGS. 12A and 12B are views showing an example where recessportions formed on a surface of a semiconductor wafer are filled.

As shown in FIG. 12A, an insulating film 2 formed of, for example, SiO₂or the like, is thinly formed on a surface of a semiconductor wafer Wincluding, for example, a silicon substrate or the like, which is anobject to be processed, and recess portions 4 are formed in theinsulating film 2. The recess portions 4 are contact holes for contactwith a lower layer or the substrate itself, through-holes, wiringgrooves, cylindrical grooves of a capacitor having a cylindricalstructure, or the like. Contact holes for contact with the substrateitself are exemplarily shown in FIG. 12A. And, as shown in FIG. 12B, aconductive thin film 6 is formed on the surface of the semiconductorwafer W in order to fill the recess portions 4. A silicon filmcontaining an impurity is often used as the thin film 6 as describedabove.

As a film formation method of forming the thin film 6, a film formationmethod (Patent Reference 1) of forming a single crystalline thin filmincluding an impurity at a low pressure of about 1 to 10⁻⁶ Pa byalternately supplying a gas including an element of silicon that is asemiconductor, for example, SiCl₄or the like, and a gas including animpurity element, such as BCl₃ or the like, a film formation method(Patent Reference 2) of alternately forming a polysilicon layer bysupplying, for example, a monosilane (SiH₄) gas, and a phosphorusadsorptive layer by supplying a phosphine gas, a film formation method(Patent Reference 3) of forming a film by CVD (Chemical VaporDeposition) by simultaneously supplying monosilane and boron trichloride(BCl₃), and so on are known.

3. Prior Art Reference

(Patent Reference 1) Japanese Patent Laid-Open Publication No. sho61-034928

(Patent Reference 2) Japanese Patent Laid-Open Publication No. hei05-251357

(Patent Reference 3) Japanese Patent Laid-Open Publication No. hei08-153688

SUMMARY OF THE INVENTION

By the way, when a request for miniaturization is not so high thatdesign rules are relatively simple, filling up the recess portions asdescribed above is favorably performed and each of the aforesaid filmformation methods has achieved good filling characteristics due to ahigh step coverage. However, as a request for miniaturization hasincreased and thus design rules become stricter in recent years,sufficient filling characteristics cannot be achieved. Also, as shownin, for example, FIG. 12B, a void 8, which is not negligible, is formedin a film, thereby increasing a contact resistance.

In particular, recently, as a strict design rule in which a holediameter of each of recess portions 4 is equal to or less than 40 nm andan aspect ratio of each of the recess portions 4 is equal to or greaterthan 10 is requested, there is a demand for a method for solving theaforesaid problems at an early stage.

Considering the aforesaid problems, the present invention has been madeto effectively solve the problems. The present invention provides a thinfilm formation method and a film formation apparatus which can form anamorphous thin film, such as a silicon film or a silicon germanium filmcontaining an impurity, having good filling characteristics even at arelatively low temperature.

An embodiment of present invention provides the thin film formationmethod to form the silicon film containing an impurity on the surface ofan object to be processed in the process chamber that allows vacuumexhaust, the thin film formation method includes supplying thesilane-based gas composed of silicon and hydrogen into the processchamber in the state that the silane-based gas is adsorbed onto thesurface of the object without supplying the impurity-containing gas,supplying the impurity-containing gas into the process chamber to formthe amorphous silicon film containing the impurity without supplying thesilane-based gas, and performing the supplying of the silane-based gasand the supplying of the impurity-containing gas alternately andrepeatedly such that the impurity reacts with the silane-based gas.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention.

The objects and advantages of the invention may be realized and obtainedby means of the instrumentalities and combinations particularly pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the the invention.

FIG. 1 is a structural view showing an example of a first embodiment ofa film formation apparatus for performing a method of the presentinvention;

FIG. 2 is a timing chart showing an example of each gas supply type in afirst embodiment of the method of the present invention;

FIG. 3 is a flowchart showing an example of each process of the firstembodiment of the method of the present invention;

FIGS. 4A through 4C are views schematically showing a reaction processbetween SiH₄ and BCl₃;

FIG. 5 is a view schematically showing an electron micrograph when anamorphous silicon film doped with boron is formed in recess portions byusing an ALD method;

FIG. 6 is a structural view showing an example of a second embodiment ofa film formation apparatus.

FIG. 7 is a timing chart showing an example of each gas supply type in asecond embodiment of the method of the present invention;

FIG. 8 is a flowchart showing an example of each process of the secondembodiment of the method of the present invention;

FIGS. 9A through 9C are views for explaining a process of a thirdembodiment of the method of the present invention;

FIG. 10 is an enlarged cross-sectional view showing an example of asemiconductor device using a thin film formed by the method of thepresent invention;

FIG. 11 is a cross-sectional view showing an upper electrode and itsvicinity for explaining a fourth embodiment of the method of the presentinvention; and

FIGS. 12A and 12B are views showing an example where recess portionsformed on a surface of a semiconductor wafer are filled.

DETAILED DESCRIPTION OF THE INVENTION Embodiments For the Invention

An embodiment of the present invention achieved on the basis of thefindings given above will now be described with reference to theaccompanying drawings. In the following description, the constituentelements having substantially the same function and arrangement aredenoted by the same reference numerals, and a repetitive descriptionwill be made only when necessary.

Hereinafter, a thin film formation method and a film formation apparatusaccording to an embodiment of the present invention will be explained indetail with reference to the attached drawings.

First Embodiment

FIG. 1 is a structural view showing an example of a first embodiment ofa film formation apparatus for performing a method of the presentinvention. As shown, the film formation apparatus 12 includes a batchtype vertical process chamber 14 having a cylindrical shape with an openlower end. The process chamber 14 may be formed of, for example, quartzwith high thermal resistance.

An open exhaust port 16 is provided in a ceiling portion of the processchamber 14, and an exhaust nozzle 18, which is bent, for example, in ahorizontal direction perpendicular to a vertical direction, iscontinuously installed in the exhaust port 16. And, a vacuum exhaustsystem 24 including a pressure control valve 20, a vacuum pump 22, orthe like is connected to the exhaust nozzle 18, so that an atmosphere inthe process chamber 14 can be evacuated due to vacuum suction.

The lower end of the process chamber 14 is supported by a manifold 26having a cylindrical shape and formed of, for example, stainless steel,and a wafer boat 28 formed of quartz is provided as a holding unit, onwhich a plurality of semiconductor wafers W which are objects to beprocessed are stacked from a lower side of the process chamber 14 atpredetermined pitches, such that the wafer boat 28 can be lowered andraised and freely inserted into and separated from the manifold 26. Asealing member 30, such as an O-ring or the like, is interposed betweenthe lower end of the process chamber 14 and an upper end of the manifold26, to hermetically maintain a space between the lower end of theprocess chamber 14 and the upper end of the manifold 26. In the presentembodiment, for example, about 50 to 100 semiconductor wafers W eachhaving a diameter of about 300 mm can be supported at substantiallyregular pitches on the wafer boat 28. Also, there may be an example ofan apparatus in which a portion of the manifold 26 is integrally moldedwith the process chamber 14 by using quartz.

The wafer boat 28 is placed on a table 34 with a Dewar flask 32 formedof quartz therebetween, and the table 34 is supported on an upper endportion of a rotating shaft 38 that penetrates through a cover 36 thatopens and closes a lower end opening of the manifold 26. And, forexample, a magnetic fluid seal 40 is installed in a portion of therotating shaft 38 penetrating through the cover 36, so that the rotatingshaft 38 is hermetically sealed and rotatably supported. Also, a sealingmember 42, such as an O-ring or the like, is installed in a lower endportion of the manifold 26 and a peripheral portion of the cover 36, sothat the inside of the process chamber 14 is sealed.

The rotating shaft 38 is attached to a front end of an arm 46 that issupported by a lifting mechanism 44, for example, a boat elevator or thelike, so that the wafer boat 28, the cover 36, and the like can beintegrally lowered and raised. Also, by fixedly installing the table 34to the cover 36, the semiconductor wafers W may be processed withoutrotating the wafer boat 28.

A heating unit 48 including a heater formed of a carbon wire isinstalled beside the process chamber 14 to surround the process chamber14, so that the semiconductor wafers W located inside the processchamber 14 can be heated. Also, a heat insulator 50 is installed at anouter periphery of the heating unit 48, so that thermal stability isensured. And, various gas supply units for introducing and supplyingvarious gases into the process chamber 14 are installed at the manifold26.

In detail, a silane-based gas supply unit 52, which supplies asilane-based gas for film formation composed of silicon and hydrogeninto the process chamber 14, and an impurity-containing gas supply unit54, which supplies an impurity-containing gas into the process chamber14, are respectively installed at the manifold 26. Also, here, ifnecessary, a support gas supply unit 56 for supplying a purge gas or apressure adjusting gas into the process chamber 14 is installed at themanifold 26. Here, a N₂ gas is used as the purge gas or the pressureadjusting gas. Also, a rare gas, such as Ar, He, or the like, may beused instead of the N₂ gas.

The silane-based gas supply unit 52, the impurity-containing gas supplyunit 54, and the support gas supply unit 56 respectively include gasnozzles 52A, 54A, and 56A which penetrate through a side wall of themanifold 26 and have front end portions extending into the processchamber 14. Gas passages 62, 64, and 66 are respectively connected tothe gas nozzles 52A, 54A, and 56A, and opening/closing valves 62A, 64A,and 66A and flow rate controllers 62B, 64B, and 66B, such as mass flowcontrollers, are sequentially installed in the gas passages 62, 64, and66, so that a silane-based gas, an impurity-containing gas, or a N₂ gasflows at controlled flow rates. Here, a silane-based gas composed ofsilicon and hydrogen as described, that is, a silane-based gas composedof only silicon and hydrogen, for example, monosilane, is used as thesilane-based gas, a BCl₃ gas is used as the impurity-containing gas, andthe N₂ gas is used as a purge gas or a pressure adjusting gas.

And, a control unit 70 including, for example, a micro computer or thelike, is installed in the film formation apparatus in order to controlthe supply of each gas to be started or stopped, a process temperature,a process pressure, and so on, or in order to control an overalloperation of the film formation apparatus. The control unit 70 includesa storage medium 72 in order to store a program used to control anoperation of the film formation apparatus 12. The storage medium 72includes, for example, a flexible disc, a CD (Compact Disc), a harddisc, a flash memory, a DVD, or the like.

Next, a first embodiment of a film formation method of the presentinvention which is performed by using the film formation apparatus 12 ofthe first embodiment constructed as described above will be explained.Each operation described below is performed under the control of thecontrol unit 70 including a computer as described above.

FIG. 2 is a timing chart showing an example of each gas supply type inthe first embodiment of the method of the present invention, FIG. 3 is aflowchart showing an example of each process of the first embodiment ofthe method of the present invention, and FIGS. 4A through 4C are viewsschematically showing a reaction process between SiH₄ and BCl₃. Themethod of the present invention forms an amorphous silicon filmcontaining an impurity by alternately and repeatedly performing a firstgas supply process in which a silane-based gas composed of silicon andhydrogen is supplied into the process chamber 14 in a state that thesilane-based gas is adsorbed onto a surface of the semiconductor wafer Wand a second gas supply process in which an impurity-containing gas issupplied into the process chamber 14.

In the timing chart of FIG. 2, a portion where a pulse is high meansthat a gas is being supplied. In detail, a first gas supply process (S1of FIG. 3) is first performed by supplying, for example, a SiH₄(monosilane) gas, as a silane-based gas into the process chamber 14 (seea timing chart (A) of FIG. 2). In the first gas supply process, themonosilane gas is supplied in a state that the monosilane gas isadsorbed onto a surface of a semiconductor wafer W that is an object tobe processed. Next, a purging process (S2 of FIG. 3) in which aremaining gas in the process chamber 14 is removed is performed (see atiming chart (C) of FIG. 2). Also, the purging process may be omitted.

Next, a second gas supply process (S3 of FIG. 3) is performed bysupplying, for example, a BCl₃ gas, as an impurity-containing gas intothe process chamber 14 (see a timing chart (B) of FIG. 2). Accordingly,the BCl₃ gas reacts with SiH₄ adsorbed onto the surface of thesemiconductor wafer W to form a very thin silicon film doped with boron(B) having a thickness of, for example, a 1 atomic level.

Next, a purging process (S4 of FIG. 3) in which a remaining gas in theprocess chamber 14 is removed is performed again (see the timing chart(C) of FIG. 2). Also, the purging process may be omitted. And, in stepS5 of FIG. 3, it is determined whether the number of times a 1 cycleincluding the steps S1 through S4 is repeated reaches a predeterminednumber of times. Here, the 1 cycle refers to a period of time from whena first gas supply process (S1) is performed to when a next first gassupply process (S1) is performed.

If it is determined in the step S5 that the number of times the 1 cycleis repeated does not reach the predetermined number of times (NO of S5),the method returns to the step S1 and the steps S1 through S4 arerepeatedly performed until the number of times the 1 cycle is repeatedreaches the predetermined number of times, to stack an amorphous siliconfilm doped with boron. And, if the number of times the 1 cycle isrepeated reaches the predetermined number of times (YES of S5), filmformation is finished. The film formation method is called a so-calledALD (Atomic Layer Deposition).

Actually, first, a plurality of semiconductor wafers W which are notprocessed yet are supported on the wafer boat 28 in a multistage manner,are transferred from the lower side of the process chamber 14 into theprocess chamber 14, which is previously heated, and are housed in asealed state. A diameter of each of the semiconductor wafers W is, forexample, 300 mm, and here, about 50 to 100 units of the semiconductorwafer W are housed. On a surface of each of the semiconductor wafers W,in a previous process, for example, an insulating layer 2 is formed asdescribed above with reference to FIGS. 12A and 12B, and recess portions4, such as contact holes or wiring grooves, are formed in the insulatinglayer 2.

An atmosphere in the process chamber 14 is always vacuum sucked by thevacuum exhaust system 24 during film formation and thus a pressure inthe process chamber 14 is adjusted. Also, the semiconductor wafer W isrotated at a predetermined rate during film formation by rotating thewafer boat 28. And, various gases are sequentially and repeatedlysupplied into the process chamber 14 as described above to perform thefilm formation. In the first gas supply process (51), the monosilane gasis supplied at a controlled flow rate from the gas nozzle 52A of thesilane-based gas supply unit 52. The monosilane gas is adsorbed onto thesurface of the semiconductor wafer W that is rotated while being raisedin the process chamber 14, and a residual gas is evacuated by the vacuumexhaust system 24 through the exhaust port 16 and the exhaust nozzle 18of an upper portion of the process chamber 14.

Process conditions at this time are as follows: a flow rate of themonosilane gas ranges from 100 to 4000 sccm, and is, for example, about1200 sccm, a process pressure ranges from 27 to 6665 Pa (0.2 to 50Torr), and is, for example, about 533 Pa (4 Torr), a process temperatureranges from 350 to 600° C., and is, for example, about 400° C., and agas supply period of time T1 ranges from 1 to 300 sec, and is, forexample, about 60 sec.

Here, if the process temperature is lower than 350° C., it is notpreferable because it is difficult for monosilane to be adsorbed ontothe surface of the semiconductor wafer W. Also, if the processtemperature is higher than 600° C., it is not preferable becausemonosilane is thermally decomposed and a silicon film is deposited.Also, if the process pressure is lower than 27 Pa, it is not preferablebecause the pressure is too low that it is difficult for monosilane tobe adsorbed. Also, if the process pressure is higher than 6665 Pa, it isnot preferable because a plurality of layers of monosilane are adsorbedand it is difficult to control a concentration of boron in the film.

In the purging process (S2) right after the first gas supply process, aN₂ gas is supplied at a controlled flow rate from the gas nozzle 56A ofthe support gas supply unit 56. Here, the N₂ gas is used as a purge gasto remove a remaining monosilane gas in the process chamber 14. Here,the N₂ gas is not supplied for an entire period of the purging process,but is supplied for a specific period, for example, the N₂ gas issupplied for the first half period and is not supplied for the secondhalf period during which only vacuum suction is continuously performed.

Process conditions at this time are as follows: a flow rate of the N₂gas is, for example, up to about 5 slm, a process pressure ranges from27 to 6665 Pa, a process temperature ranges from 350 to 600° C., and apurging period of time T2 ranges from 0 to 300 sec and is, for example,about 30 sec. In the second gas supply process (S3) after the purgingprocess, the BCl₃ gas is supplied at a controlled flow rate from the gasnozzle 54A of the impurity-containing gas supply unit 54. At the sametime, a N₂ gas is supplied as a pressure adjusting gas at a controlledflow rate from the gas nozzle 56A of the support gas supply unit 56 (seethe timing chart (C) of FIG. 2). The BCl₃ gas and the N₂ gas are raisedin the process chamber 14, and the BCl₃ gas reacts with the monosilaneadsorbed onto the surface of the semiconductor wafer W to form anamorphous silicon film containing boron. And, a residual gas isevacuated by the vacuum exhaust system 24 through the exhaust port 16and the exhaust nozzle 18 of an upper portion of the process chamber 14.

Process conditions at this time are as follows: a flow rate of the BCl₃gas ranges, for example, from 1 to 500 sccm, and is, for example, about100 sccm, a flow rate of the N₂ gas is up to about 5 slm, a processpressure ranges from 27 to 6665 Pa (0.2 to 50 Torr) and is, for example,about 533 Pa (4 Torr), a process temperature ranges from 350 to 600° C.and is, for example, about 400° C., and a gas supply period of time T3ranges from 1 to 300 sec and is, for example, about 60 sec.

Here, if the process temperature is lower than 350° C., it is notpreferable because it is difficult for BCl₃ to react with the monosilaneadsorbed onto the surface of the semiconductor wafer W, and if theprocess temperature is higher than 600° C., it is not preferable becausea time is taken to increase temperature.

In the purging process (S4) right after the second gas supply process, aN₂ gas is supplied at a controlled flow rate from the gas nozzle 56A ofthe support gas supply unit 56 in the same manner as that in the purgingprocess of the step S2. Actually, the N₂ gas is continuously suppliedsince the second gas supply process. Here, the N₂ gas is used as a purgegas, to remove a remaining BCl₃ gas in the process chamber 14. Here, theN₂ gas is not supplied for an entire period of the purging process, butis supplied for a specific period, for example, the N₂ gas is suppliedfor the first half period and is not supplied for the second half periodduring which only vacuum suction is continuously performed.

Process conditions at this time are the same as those in the purgingprocess of the step S2. That is, a flow rate of the N₂ gas is, forexample, up to about 5 slm. A process pressure ranges from 27 to 6665Pa, a process temperature ranges from 350 to 600° C., and a purgingperiod of a time T4 ranges from 0 to 300 sec and is, for example, about30 sec.

The 1 cycle including processes of the steps S1 through S4 is repeatedlyperformed only a predetermined number of times. Although the number ofcycles depends on a target film thickness of a film to be formed, sincefilm formation is performed to have a film thickness of, for example,about 0.2 to 0.7 nm, during a 1 cycle, if a film thickness of, forexample, about 60 nm is needed, 100 cycles are performed. As describedabove, a thin film such as a very thin amorphous silicon film having athickness of an atomic level and doped with B (boron) as an impurity isstacked, so that the silicon film can be filled with good fillingcharacteristics in the recess portions 4 (see FIGS. 12A and 12B) formedon the surface of the semiconductor wafer W.

Here, a film formation process of an amorphous silicon film doped withboron generated during the film formation will be explained withreference to a schematic view shown in FIGS. 4A through 4C. FIGS. 4Athrough 4C are views schematically showing results obtained whensimulating a film formation process of an amorphous silicon film dopedwith boron by using quantum chemical calculation. An activation energyeV is shown under each picture. Here, particularly, the possibility oflow temperature film formation by using alternate supply (ALD method)using SiH₄ and BCl₃ was verified by a simulation.

First, when SiH₄ introduced from the outside approaches a Si—B bondingthat is already formed on a surface of a semiconductor wafer (see FIG.4A), due to a catalysis by B atom, as shown in FIG. 4B, H₂ is removedfrom SiH₄ to generate SiH₂ which is easily introduced into a B-adsorbingspot. In detail, an activation energy of SiH₂ to the B-adsorbing spot isreduced to about 1.2 eV. Also, if B (boron) does not exist, anactivation energy is about +2.4 eV. Next, as shown in FIG. 4C, a Si—Sibonding is continuously formed.

In this regard, it is deemed that since film formation is possible at alow temperature of about 350° C. at which practical film formation wasimpossible with supply of only SiH₄ in a conventional art, and ALD filmformation is performed by alternately supplying gases, a thin filmhaving a good step coverage is obtained.

Meanwhile, in a conventional CVD method in which only SiH₄ is used,practical film formation was almost impossible. Also, in a CVD methodusing only Si₂H₆, although film formation was possible even at a processtemperature of 400° C., a step coverage thereof was about 80%, therebyfailing to have excellent results.

As such, in the thin film formation method of forming a silicon filmcontaining an impurity on the surface of the semiconductor wafer W inthe process chamber 14 that allows vacuum exhaust, an amorphous siliconfilm containing an impurity is formed by alternately and repeatedlyperforming the first gas supply process in which a silane-based gascomposed of silicon and hydrogen is supplied into the process chamber 14in a state the silane-based gas is adsorbed onto the surface of thesemiconductor wafer W and the second gas supply process in which animpurity-containing gas is supplied into the process chamber 14, andthereby an amorphous silicon film containing an impurity having goodfilling characteristics can be formed even at a relatively lowtemperature.

Evaluation of the Method of the Present Invention

Here, since an amorphous silicon film doped with boron was formed byactually performing the method of the present invention, evaluationresults thereof will be explained. Here, a silicon substrate was used asa semiconductor wafer, a silicon oxide film was formed as a base layeron a surface of the silicon substrate, and recess portions each having ahole diameter of 50 nm and an aspect ratio of 7 were formed in thesilicon oxide film. And, an amorphous silicon film doped with boron asan impurity was formed on the silicon oxide film.

As a film formation method, the film formation method described abovewith reference to the timing charts (A) through (C) of FIG. 2 was used.SiH₄ was used as a silane-based gas, and BCl₃ was used as animpurity-containing gas. Process conditions were as follows: a flow rateof a SiH₄ gas was 2000 sccm, a flow rate of a BCl₃ gas was 200 sccm, anda flow rate of a N₂ gas was 2 slm when being used as a purge gas and was1 slm when being used as a pressure adjusting gas. A process temperaturewas set to 400° C. throughout the method, and a process pressure in eachof the first gas supply process and the second gas supply process was533 Pa (4 Torr). A process period of time T1 was 30 sec, T2 was 30 sec,T3 was 30 sec, and T4 was 30 sec.

As such, after film formation was performed on a wafer having a surfacehaving a trench structure, an amorphous silicon film doped with boron of180 Å was obtained after 60 cycles. Results in this case are shown inFIG. 5. FIG. 5 is a view schematically showing an electron micrographwhen an amorphous silicon film doped with boron is formed in recessportions by using an ALD method as described above. Here, a diameter ofeach of the recess portions is 50 nm, and also, an aspect ratio (A/R) ofeach of the recess portions is “7”. In FIG. 5, film thicknesses alonginsides of the recess portions are shown. It is found from FIG. 5 that astep coverage is equal to or greater than 95% which are excellentresults.

Also, although, in the first embodiment of the film formation method, aN₂ gas is supplied as a purge gas in the purging processes T2 and T4 andis supplied as a pressure adjusting gas in the second gas supply processas shown in the timing chart (C) of FIG. 2, the present invention is notlimited thereto, and the N₂ gas may be supplied as described below.Timing charts (D) through (F) of FIG. 2 show a modified example of a N₂gas supply type. In the timing chart (D) of FIG. 2, unlike in the timingchart (C) of FIG. 2, a N₂ gas is not supplied for the first half periodin both purging processes before and after a second gas supply process,but is supplied for the second half period. And, in the second gassupply process, like in the timing chart (C) of FIG. 2, the N₂ gas issupplied as a pressure adjusting gas.

In the timing chart (E) of FIG. 2, a N₂ gas is supplied in both purgingprocesses before and after the second gas supply process in the samemanner as that in the timing chart (C) of FIG. 2, and in the second gassupply process, the N₂ gas (pressure adjusting gas) is not supplied.Also, in the timing chart (D) of FIG. 2, a N₂ gas may not be supplied inthe second gas supply process.

In the timing chart (F) of FIG. 2, unlike the above, a N₂ gas (purgegas) is not supplied for an entire period of both purging processesbefore and after the second gas supply process, and in the second gassupply process, the N₂ gas (pressure adjusting gas) is supplied in thesame manner as that in the timing chart (C) of FIG. 2. As such, a purgegas or a pressure adjusting gas may be supplied in various manners. Thereason why a pressure adjusting gas is supplied in the second gas supplyprocess as described above is that if a pressure is changed drasticallyin first and second gas supply processes, silicon migration easilyoccurs.

Second Embodiment

Next, a second embodiment of the film formation apparatus and the thinfilm formation method of the present invention will be explained. Whilean amorphous silicon film containing an impurity is formed in the firstembodiment, an amorphous silicon germanium film containing an impurityis formed in the second embodiment.

FIG. 6 is a structural view showing an example of the second embodimentof the film formation apparatus, FIG. 7 is a timing chart showing anexample of each gas supply type in the second embodiment of the methodof the present invention, and FIG. 8 is a flowchart showing an exampleof each process of the second embodiment of the method of the presentinvention. Also, in FIGS. 6 through 8, the same portions as those shownin FIGS. 1 through 3 are denoted by the same reference numerals, and anexplanation thereof will not be given.

As shown in FIG. 6, a film formation apparatus 12 according to thesecond embodiment, in order to form an amorphous silicon germanium filmcontaining an impurity as a thin film as described above, includes agermanium-based gas supply unit 80 as gas supply units in addition tothe silane-based gas supply unit 52, the impurity-containing gas supplyunit 54, and the support gas supply unit 50 described above. Thegermanium-based gas supply unit 80, like the other gas supply systems,includes a gas nozzle 80A that penetrates through a side wall of themanifold 26 and has a front end portion extending into the processchamber 14.

A gas passage 82 is connected to the gas nozzle 80A, and anopening/closing valve 82A and a flow rate controller 82B, such as a massflow controller, are sequentially installed in the gas passage 82, sothat a germanium-based gas flows at a controlled flow rate. Thegermanium-based gas may include at least one gas selected from the groupconsisting of a GeH₄ gas, a GeH₆ gas, and a Ge₂H₆ gas, and herein theGeH₄ gas is used.

In the second embodiment of the film formation method performed by usingthe film formation apparatus 12 of the second embodiment, as shown inFIGS. 7 and 8, a GeH₄ gas (see a timing chart (D) of FIG. 7 and S1 ofFIG. 8) is supplied into the process chamber 14 at the same time and inthe same period with a SiH₄ gas that is a silane-based gas. That is, theGeH₄ gas is supplied in a first gas supply process (T1) of each cycleshown in FIG. 7, and film formation is performed by using an ALD methodlike in the first embodiment. Accordingly, boron (B) is introduced as animpurity into a film formed of silicon and germanium, thereby forming anamorphous silicon germanium film containing boron.

In this case, a purging process is performed in the same manner as thatdescribed in the first embodiment with reference to FIG. 2 and so on.Also, process conditions, for example, a process pressure, a processtemperature, and a flow rate of each gas, in a first gas supply process,a second gas supply process, and a purging process, are the same asthose described in the first embodiment. In this case, a flow rate of agermanium-based gas in the first gas supply process ranges from 100 to2000 sccm, and is, for example, about 500 sccm.

Also, it would be understood that although various N₂ gas supply typeshave been explained in the first embodiment with reference to the timingcharts (D) through (F) of FIG. 2, the various supply types may apply tothe second embodiment.

As such, in a thin film formation method to form a silicon germaniumfilm containing an impurity on a surface of an object to be processed inthe process chamber 14 that allows vacuum exhaust, an amorphous silicongermanium film containing an impurity is formed by alternately andrepeatedly performing a first gas supply process in which a silane-basedgas composed of silicon and hydrogen and a germanium-based gas composedof germanium and hydrogen are supplied into the process chamber 14 in astate that the silane-based gas and the germanium-based gas are adsorbedonto the surface of the semiconductor wafer W and a second gas supplyprocess in which an impurity-containing gas is supplied into the processchamber 14, and thereby an amorphous silicon germanium film containingan impurity having good filling characteristics can be formed even at arelatively low temperature.

Third Embodiment

Next, a third embodiment of the method of the present invention will beexplained. While an amorphous silicon film doped with boron is formed asa thin film in the first embodiment and an amorphous silicon germaniumfilm doped with boron is formed as a thin film in the second embodimentin the film formation method as described above, a combination thereofmay be possible. FIGS. 9A through 9C are views for explaining a processof the third embodiment of the method of the present invention. Here, acase where each thin film is formed on a conductive film and then anannealing process is additionally and finally performed will beexemplarily explained.

First, as shown in FIG. 9A, a conductive film 90 is formed on a surfaceof a semiconductor wafer W as an object to be processed. For example, aTiN film or the like which is often used as an electrode is used as theconductive film 90. An amorphous silicon film 92 doped with boron isformed as a thin film on the conductive film 90 by using the firstembodiment or its modified embodiment of the film formation method.

Next, as shown in FIG. 9B, an amorphous silicon germanium film 94 dopedwith boron is formed as a thin film on the silicon film 92 by using thesecond embodiment or its modified example of the film formation method.Here, a thickness of the silicon film 92 is equal to or less than, forexample, 2 nm, and a thickness of the silicon germanium film 94 is equalto or less than, for example, 90 nm. In this case, if the film formationapparatus of the second embodiment shown in FIG. 6 is used, the siliconfilm 92 and the silicon germanium film 94 can be continuously formedwith one film formation apparatus.

Next, as shown in FIG. 9C, an annealing process is performed on eachthin film to diffuse and mix germanium of the silicon germanium film 94in both the thin films 92 and 94, thereby forming a mixed film 96. Atemperature of the annealing process ranges from, for example, 410 to500° C. Also, the annealing process may be performed and may not beperformed, if necessary.

Here, since a thickness of the silicon germanium film 94 is, forexample, 90 nm which is thick, it is preferable that when the silicongermanium film 94 is formed, the silicon germanium film 94 is formed toa middle thickness, for example, about 10 nm by using the secondembodiment of the film formation method, and a silicon germanium filmdoped with boron may be formed to a remaining thickness of 80 nm byusing a CVD (Chemical Vapor Deposition) method that is a conventionalfilm formation method. Even in this case, it is preferable that anannealing process is finally performed.

As such, by forming the mixed film 96, in order to fill recess portions,for example, trench portions, if a B—Si film doped with boron is formedas a seed layer and then a B—SiGe film doped with boron is formed, agood step coverage and excellent filling characteristics can be obtainedeven at low temperature film formation.

Application Example of Semiconductor Device

Next, an application example of a semiconductor device using a thin filmformed by the method of the present invention will be explained. FIG. 10is an enlarged cross-sectional view showing an example of asemiconductor device using a thin film formed by the method of thepresent invention. A semiconductor device 100 includes, for example, acapacitor 102 having a cylindrical structure. In detail, the capacitor102 is provided in a fine cylindrical groove 104 having a recess shapeformed on a surface of a semiconductor wafer W including, for example, asilicon substrate.

That is, the capacitor 102 has a lower electrode 106 formed along aninner wall of the cylindrical groove 104 having the recess shape, and ahigh dielectric constant film 108 and an upper electrode 110 aresequentially stacked on the lower electrode 106. For example, a TiN filmmay be used as each of the lower electrode 106 and the upper electrode110, and for example, zirconium oxide (ZrO) may be used for the highdielectric constant film 108.

And, the cylindrical groove 104 is filled in by forming a conductivefilm 112 on the upper electrode 110, and a wiring film 114 including,for example, a tungsten film, is formed on the conductive film 112 byusing sputtering or the like. Here, the silicon film 92, the silicongermanium film 94, or the mixed film 96 (see FIGS. 9A through 9C) formedby the method of the present invention is used as the conductive film112 filled in the cylindrical groove 104.

When the cylindrical groove 104 of the capacitor 102 having thecylindrical structure is filled, a conventional film formation method offorming a silicon germanium film doped with boron by using, for example,a CVD method, cannot achieve a sufficient step coverage and thus is notpractical. However, by employing the film formation method according tothe method of the present invention as described above, the cylindricalgroove 104 can be filled with a high step coverage.

Also, due to the thin film formed by the method of the present inventionas described above, that is, the silicon film 92, the silicon germaniumfilm 94, or the mixed film 96, durability against mechanical stressbetween the wiring film 114 formed by using sputtering and the upperelectrode 110 formed of a TiN film can be improved.

Fourth Embodiment

Next, a fourth embodiment of the method of the present invention will beexplained. Although the amorphous silicon film 92 doped with boron orthe like is formed on the upper electrode 110 formed of, for example, aTiN film, in the application example of the semiconductor device shownin FIG. 10, here, a stacked structure obtained by alternately stacking aplurality of times a TiN film as the upper electrode 110 and theamorphous silicon film 92 doped with boron may be employed. Accordingly,a stress of the upper electrode 110 itself can be reduced.

FIG. 11 is a cross-sectional view showing an upper electrode and itsvicinity for explaining the fourth embodiment of the method of thepresent invention. Here, only order of stacking films is shown and acylindrical groove is not shown. Also, the same portions as those in thestacked structure shown in FIG. 10 are denoted by the same referencenumerals.

In the fourth embodiment, instead of a thick TiN film as the upperelectrode 110 as described above, a stacked film 122 obtained byalternately and repeatedly forming a plurality of times a thin TiN film120 as shown in FIG. 11 and the thin amorphous silicon film 92 dopedwith boron formed by the method of the present invention is used. InFIG. 11, although the TiN film 120 and the silicon film 92 arerepeatedly formed 3 times, the number of times the TiN film 120 and thesilicon film 92 are formed is not specially limited. In the upperelectrode 110 of FIG. 11, a thickness of one layer of the silicon film92 is, for example, about 5 to 15 nm, and a thickness of one layer ofthe TiN film 120 is, for example, about 5 to 20 nm.

In order to form the TiN film 120, a titan-containing gas supply unitand a nitridation gas supply unit may be provided in the film formationapparatus shown in FIG. 1 or 6, and these gases may be supplied atcontrolled flow rates. For example, a TiCl₄ gas may be used as thetitan-containing gas, and a NH₃ gas may be used as the nitridation gas,but the present invention is not limited to the gas types. The TiN film120 may be formed by using a CVD method by supplying both the gases atthe same time into the process chamber, or may be formed by using an ALDmethod by alternately and repeatedly supplying both the gases into theprocess chamber.

Accordingly, as described above, a stress of the upper electrode 110itself can be reduced. Also, the upper electrode 110 including thestacked film 122 and the conductive film 112 may be continuously formedin the same film formation apparatus. Also, on the upper electrode 110including the stacked film 122, as described in FIG. 10, the siliconfilm 92, the silicon germanium film 94, or the mixed film 96 may bestacked as the conductive film 112.

Also, although an N₂ gas is intermittently supplied in each embodimentof the film formation method, the present invention is not limitedthereto, and the N₂ gas may be continuously supplied for an entireperiod of film formation, so as not to greatly change a pressure.

Also, although an N₂ gas is used as a purge gas in each purging processor as a pressure adjusting gas in the second gas supply process in eachembodiment of the film formation method, a rare gas, such as Ar, He, orthe like, may be used instead of the N₂ gas. Also, although an N₂ gas isused as a purge gas in each purging process or as a pressure adjustinggas in the second gas supply process in each embodiment of the filmformation method, a H₂ gas may be used alone or by being mixed with theN₂ gas or the rare gas, instead of the N₂ gas or the rare gas. Inparticular, if the H₂ gas is used, the H₂ gas suppresses siliconmigration to prevent particles of a silicon film from being attached,thereby further improving filling characteristics.

Although a pressure adjusting gas is mainly supplied in the second gassupply process in each embodiment of the film formation method, apressure adjusting gas may be supplied in the first gas supply processinstead of the second supply process, or in both the first and secondgas supply processes. Also, although monosilane is exemplarily used as asilane-based gas composed of silicon and hydrogen in each embodiment,the present invention is not limited thereto, and one or more types ofgas selected from the group consisting of monosilane and higher ordersilane such as disilane, trisilane, tetrasilane, or the like may beused.

Also, although a BCl₃ gas is used in order to contain an impurity(dopant) in an amorphous silicon film or a silicon germanium film ineach embodiment of the film formation method, the present invention isnot limited thereto, and one or more types of gas selected from thegroup consisting of BCl₃, PH₃, PF₃, AsH₃, PCl₃, and B₂H₆ may be used asthe impurity-containing gas and various impurities may be doped.

Also, although as shown in FIGS. 1 and 6, a single-tube batch type filmformation apparatus in which the process chamber 14 is provided in asingle layer is exemplarily explained here, the present invention is notlimited thereto, and the present invention can be applied to adouble-tube batch type film formation apparatus in which the processchamber 14 includes an inner container and an outer container. Also,although the gas nozzles 52A, 54A, 56A, and 80A are each a straight-typegas nozzle in which a gas is ejected only from a leading end of the gasnozzle, the present invention is not limited thereto, and a so-calleddistribution-type gas nozzle in which a plurality of gas ejection holesare provided at predetermined pitches in a gas pipe disposed along alongitudinal direction of the process chamber 14 and a gas is ejectedfrom each of the gas ejection holes may be used.

Also, although a batch type film formation apparatus which processes aplurality of semiconductor wafers W at one time as described above isexemplarily explained, the present invention is not limited thereto, andthe present invention can be applied to a so-called single wafer typefilm formation apparatus which processes one semiconductor wafer W.

Also, although, here, a semiconductor wafer is exemplarily explained asan object to be processed, the semiconductor wafer may be a siliconsubstrate, or a compound semiconductor substrate, such as GaAs, SiC,GaN, or the like, and also the present invention is not limited thereto,and the present invention can be applied to a glass substrate used in aliquid crystal display device, a ceramic substrate, and so on.

The thin film formation method and the film formation apparatusaccording to the present invention can have the following excellenteffects.

According to an embodiment of the present invention, in the thin filmformation method to form the silicon film containing an impurity on thesurface of an object to be processed in the process chamber that allowsvacuum exhaust, the thin film formation method includes supplying thesilane-based gas composed of silicon and hydrogen into the processchamber in the state that the silane-based gas is adsorbed onto thesurface of the object without supplying the impurity-containing gas,supplying the impurity-containing gas into the process chamber to formthe amorphous silicon film containing the impurity without supplying thesilane-based gas, and performing the supplying of the silane-based gasand the supplying of the impurity-containing gas alternately andrepeatedly such that the impurity reacts with the silane-based gas, andthereby the amorphous silicon film containing an impurity having goodfilling characteristics can be formed even at a relatively lowtemperature.

What is claimed is:
 1. A thin film formation method to form an amorphoussilicon film containing an impurity on a surface of an object to beprocessed in a process chamber that allows vacuum exhaust, the methodcomprising: supplying a silane-based gas composed of silicon andhydrogen into the process chamber in a state that the silane-based gasis adsorbed onto the surface of the object without supplying animpurity-containing gas; supplying the impurity-containing gas into theprocess chamber to form the amorphous silicon film containing theimpurity without supplying the silane-based gas; and performing thesupplying of the silane-based gas and the supplying of theimpurity-containing gas alternately and repeatedly such that theimpurity reacts with the silane-based gas.
 2. The thin film formationmethod of claim 1, wherein a process temperature in each of thesupplying of the silane-based gas and the supplying of theimpurity-containing gas ranges from 350 to 600° C.
 3. The thin filmformation method of claim 1, wherein a process pressure in each of thesupplying of the silane-based gas and the supplying of theimpurity-containing gas ranges from 27 to 6665 Pa (0.2 to 50 Torr). 4.The thin film formation method of claim 1, further comprising performinga purging process, in which a remaining gas in the process chamber isremoved, between the supplying of the silane-based gas and the supplyingof the impurity-containing gas.
 5. The thin film formation method ofclaim 4, wherein in an entire or specific period of the purging process,a purge gas for accelerating removal of the remaining gas is supplied.6. The thin film formation method of claim 1, wherein the silane-basedgas comprises one or more types of gas selected from a group consistingof monosilane and higher order silane.
 7. The thin film formation methodclaim 1, wherein the impurity-containing gas comprises one or more typesof gas selected from a group consisting of BCl₃, PH₃, PF₃, AsH₃, PCl₃,and B₂H₆.